This invention generally relates to removal of polymer residues following an etching process and more particularly to an in-situ wet polymer stripping (PRS) apparatus and processes whereby polymer residues are removed following an etching process.
In the fabrication of semiconductor devices multiple layers may be required for providing a multi-layered interconnect structure. During the manufacture of integrated circuits it is common to place material photoresist on top of a semiconductor wafer in desired patterns and to etch away or otherwise remove surrounding material not covered by the resist pattern in order to produce metal conductor runs or other desired features. During the formation of semiconductor devices it is often required that the conductive layers be interconnected through holes in an insulating layer. Such holes are commonly referred to as contact holes, i.e., when the hole extends through an insulating layer to an active device area, or vias, i.e., when the hole extends through an insulating layer between two conductive layers. The profile of a hole is of particular importance since that it exhibits specific electrical characteristics when the contact hole or via is filled with a conductive material.
In anisotropic etching processes, such as those using halocarbon containing plasmas, polymer deposition on the sidewalls and bottom surface of the contact hole or via being etched occurs simultaneously with the etching of the oxide or the metal, as the case may be. Surfaces struck by the ions at a lower rate tend to remove the nonvolatile polymeric residual layer at a lower rate, thereby at steady state, leaving a layer of nonvolatile polymeric or metal-polymeric residue on surfaces such as the sidewalls of the etched opening, thereby protecting such surfaces against etching by the reactive gas. As such, etching is performed preferentially in a direction perpendicular to the wafer surface since the bottom surfaces etch at a higher rate than the polymeric residue containing sidewalls (i.e., anisotropic etching). If metal is being etched, for example, in the case where an oxide is etched through to expose an underlying metal layer, metal will simultaneously deposit with the polymer thus forming a metal-polymer residue on the sidewalls of the etched opening.
In a typical process, for example, in a via hole etch process, an inter-metal dielectric (IMD) layer is provided over a metallic contact layer, and a photoresist layer is provided over the IMD layer, the photoresist layer being patterned for etching through the IMD layer to the metal contact layer.
After the via holes are etched, but before the holes are filled with a conductive material, the photoresist mask which remains on top of the desired features may be removed by a dry etching method known as a reactive ion etch (RIE) or ashing process in a quartz chamber using a plasma of O2 or a combination of CF4 and O2 to react with the photoresist material.
It has been the practice in the art to remove at least the photoresist in-situ by an ashing process following an etching procedure where metal is exposed, for instance after etching through the IMD layer to the metal conductive layer, since exposure of the metal to atmospheric conditions can cause metallic corrosion. In such an in-situ ashing process, the photoresist removal may take place by a reactive ion etching (RIE) method using an oxygen containing plasma in a stripper chamber module of a metal etcher such as, for example, the LAM TCP 9600 DSQ Stripper Chamber. The LAM Research TCP 9600 single wafer metal etcher is an example of a state-of-the-art single wafer RIE or plasma etch tool for etching metal conductor patterns, such as aluminum or aluminum-silicon-copper alloys. The Stripper Chamber is just one module in a series of modules included a metal etching apparatus as in, for example, the LAM TCP 9600.
A representative schematic layout of a series of modules for metal etching and photoresist stripping in a typical metal etching apparatus is shown in FIG. 1. In a typical process, a wafer is inserted into the load indexer 10, from which it is remotely transferred to the wafer orienter 12, as indicated by an arrow representing process flow direction, then to the entrance loadlock module 14, and finally to the reaction chamber module 16 where the main etching process takes place including metal etching. After etching, the wafer is moved downstream to a DSQ (DownStream Quartz) asher/stripper module 18 where the photoresist mask is removed by an ashing process involving a reactive ion etch (RIE) using an oxygen containing plasma. Following the ashing process, the wafer substrate is transferred to the APM (Atmospheric Passivation Module) 20 where it is rinsed in a deionized water bath 21 supplied through deionized water supply 22 through line 23 to remove any residual halogens from the metal etching process such as chlorine. Finally the wafer substrate is transferred to the unload indexer 24 for unloading of the wafer.
Maximum efficiency for such an in-line processing is obtained when processes are simultaneously performed in both chambers and when the process times for each chamber (module) are approximately equal, so that one of the chambers does not stand idle while awaiting completion of the process in the other chamber.
A processing difficulty arises, however, when a metal-polymer residue forms upon etching for example, a via hole. In a typical etching process, etching takes place through the inter-metal dielectric (IMD) layer to expose an underlying metallic contact. Typically the metallic portion is over etched to assure adequate contact of the via hole (which will later be filled with a metallic material) with the underlying metal contact layer. As a result, during the etching process, a metal-polymer residue is formed on the sidewalls of an etched opening that cannot be removed by the reactive ion etching (RIE) or ashing process.
Further, the RIE process to remove the overlying photoresist may tend to oxidize the metal-polymer residue formed on the sidewalls of an etched opening thereby making it even more resistant to an RIE cleaning process. As a result, the metal-polymer residue formed on the sidewalls of an etched opening cannot be successfully removed by an RIE process and must be removed by a wet process. It has been found necessary in the art to remove the process wafers from the metal etcher, to subject the process wafers with the metal-polymer residue to a wet polymer strip process (PRS) to remove the metal-polymer residue.
Since frequently, semiconductor device processing includes many layers that must be interconnected by vias or metal contact holes, removing a wafer from the metal etcher for wet chemical stripping or polymer stripping (PRS) to remove the metal-polymer residue remaining after each process where a metal layer is partially etched, can prove very time consuming when, for example, a 0.15 micron logic device with seven (7) metal layers is manufactured. In this case, for example, a throughput can be calculated to be about 1.5 hours per metal layer or alternatively, more than 12 hours per wafer lot.
Other drawbacks of an ex-situ wet polymer strip process (PRS), using for example a wet bench setup, include the possibility of particle contamination of the wafer upon removal from the metal etcher. Further, since adequate metal-polymer residue removal may require more than one process station where the wafer is immersed into a chemical solution, the chemical cost may be high.
FIG. 2 shows a typical wet polymer strip process (PRS) bench configuration 200. In a typical wet polymer strip process, wafers are loaded into a loading module 201, transferred to a wet bench process line beginning with a mounting station 202. The wafer is typically immersed in a plasma etching cleaning solution at one or more stations e.g., 204A, 204B, using for example, ACT (e.g., 690C) available from Ashland Chemical composed of DMSO (Dimethyl-sulphur-oxuide), MEA (Mono-Ethyl-Amine) and catechol. The wafers are then typically immersed in a neutralizing solution of n-methyl pyrrolidone (NMP) at station 206, followed by a QDR (quick dump rinse) in water at station 208, a soak in water at one or more pool stations e.g., 210A, 210B, and finally to a drying station 212, before unloading at unloading module 214. The sequence among the various washing modules can be programmed and can be out of order. As previously mentioned, the ex-situ wet polymer strip process (PRS) greatly reduces the efficiency and processing throughput in manufacturing process where metal etching is performed.
There is therefore a need in the semiconductor processing art to develop an improved cleaning apparatus and method whereby metal-polymer residues following an RIE etching process where, for example, a portion of the etched metal is deposited together with polymeric residues (i.e., metal-polymer) on the sidewalls of etched openings, can be removed faster and more efficiently giving a higher throughput.
It is therefore an object of the invention to provide an apparatus whereby a wet polymer strip process can be employed more efficiently thus increasing a throughput per metallic layer in a semiconductor manufacturing process to remove metal-polymer residues while overcoming other shortcomings and deficiencies in the prior art.
It is another object of the invention to provide a method whereby a wet polymer strip process can be employed more efficiently thus increasing a throughput per metallic layer in a semiconductor manufacturing process to remove metal-polymer residues while overcoming other shortcomings and deficiencies in the prior art.
To achieve the foregoing and other objects, and in accordance with the purposes of the present invention, as embodied and broadly described herein, the present invention provides a method and apparatus for in-situ removal of etching residues following an etching process.
In a first embodiment according to the present invention, is provided a cleaning module for removing a polymer residue from a process wafer in-situ following an etching process which includes a chamber with means for controlling an ambient disposed adjacent to a reactive ion etching chamber; a remote handling means whereby a process wafer is transferred from the reactive ion etch chamber to the wafer cleaning chamber under controllable ambient conditions; at least one solution container disposed outside the wafer cleaning chamber; at least one solution bath disposed within the wafer cleaning chamber for containing a solution whereby at least one process wafer is submersible therein for in-situ cleaning; and at least one fluidic pathway in communication with the at least one solution container and one solution bath for supplying and removing a solution to the at least one solution bath.
In a related embodiment, the at least one solution container includes a solution selected from the group consisting of etchant solution, neutralizing solution, and rinsing solution.
In another embodiment according to the present invention, at least one second fluidic pathway is in communication with the at least one solution bath for removing the at least one solution outside the wafer cleaning chamber following a period of use.
In yet another embodiment according to the present invention, the at least one second fluidic pathway is in communication with the at least one solution container for recycling at least one solution.
In yet other aspects of the invention the at least one solution bath includes a means for heating a solution contained the at least one solution bath to a predetermined temperature. Further, the at least one solution bath comprises a means for agitating a solution contained in the at least one solution bath.
In a separate embodiment according to the present invention, is provided a method for in-situ removal an etching residue to increase a process throughput comprising the steps of: providing a wafer cleaning chamber adjacent to a reactive ion etch chamber; controlling an ambient in the wafer cleaning chamber and reactive ion etch chamber; providing a remote handling means whereby a process wafer is transferred from the reactive ion etch chamber to the wafer cleaning chamber under controllable ambient conditions; transferring by remote handling means at least one process wafer following a reactive ion etch process from the reactive ion etch chamber to the wafer cleaning chamber under controllable ambient conditions; providing at least one solution container disposed outside the wafer cleaning chamber; providing at least one solution bath disposed within the wafer cleaning chamber; providing a solution in the at least one solution container; providing at least one fluidic pathway in communication with the at least one solution container and the at least one solution bath for supplying the solution to the at least one solution bath; controllably supplying the solution from the at least one solution container to the at least one solution bath; immersing the at least one process wafer into the at least one solution bath; and, drying the at least one process wafer.
These and other embodiments, aspects and features of the invention will become better understood from a detailed description of a preferred embodiment of the invention which is described in conjunction with the accompanying drawings.